Kaled Zem
This is where Dispater first emerged which suggests that deep under the mountains is/was an ancient connection to the depths of the underworld. That connection would have relied on the Astral and could be a good source of more essence.
Kaled Zem is an ancient place, much of the history is pre First Age - making it highly relevant for a world that has reset to zero. This is based on the fact that the Dwarves were already in Kaled Zem when the human-centric First Age started recording history. They were there for 500 years before Lastar was even born.
First Age
0-100 The reign of the Elves is confined to Vikriain and the Silven Lands. The Dwarven Lands comprise a series of mountain ranges which bordered the Elven realms; these mountains run southwards from Fangor Rodrus to Findor and encompass Kaled Zem, Balem and Hama’Las.
500 Lastar and The rise of Dispater. Lastar is born to a Half-elf woman (Sylvan) and a man called Eorand. The Dwarves of Kaled Zem unearth a great evil power - Dispater. The Devil unites the races of evil that inhabit the Forgotten Lands, east of the Dwarven mountains.
525 The Rise of Orcus; The Elven Gems and Bavarik. A new evil, a Demon named Orcus, rises from the Abyss and attacks the Dwarves from the North East, flattening the mountain range between Fangor Rodrus and Kaled Zem. Elves enter the battle under Lastar’s command and use their magical gems against Orcus’ army. The gems belong to the following Elves: Gelmir of the Silven Lands, Aerandir of Numenorea, Nenya of the Old Forest and Elwe of Lorial. Bavarik of Arogan is born in Gos.
535 The Rise of Demogorgan. Not yet at full strength, this young Demon visits the Prime Material Plane for the first time. Unwisely, Demogorgan stretches his forces attacking the Elves to the South of Kaled Zem, Orcus to the south east of Fangor Rodrus and the Dwarves east of Balem Lakes.
557 Minas Maedus and Minas Emras complete. The House of Rodrus is built and ruled by Maedus. The House of Zem comes to power at Minas Emras.
557 The Elemental Rings. The Rings of Power and the Elven Gems are united by Dwarven craftsmen. Lastar gives each Ring elemental powers. Hamar (living in Minas Aarda) receives the Ring of Earth. Zem (living in Minas Emras) receives the Ring of Air. Ishtur (living in Minas Morgul) receives the Ring of Fire. Dor (living in Minas Tiris) receives the Ring of Water.
557-560 Men and Dwarves build Sutur. Orodruin’s kindred move to the west of Kaled Zem. Whilst this depletes the force holding Minas Maedus, Lastar promises them help if they build a large tower and keep to protect Kaled Zem.
Second Age
671 Demogorgan Returns - A vast army of evil is arrayed on the waste lands of Amras Aarda. Findor is attacked from the south and boats land in the Bay of Ashore. A large force of strange creatures never seen before march through the gap between Fangor Rodrus and Kaled Zem, on the Planes of Eriador.
732 The Fall of Minas Aarda - Despite the aid sent from Balem and Kaled Zem, the noble house of Hamar crumbles as Demogorgan grows in might. Hamar, Lord of Aarda, dies during the battle. Demogorgan takes his Palantir but overlooks his Ring.
780 The 5th Crown and Balor - The Crown lay hidden at the foot of a large waterfall that fell out of Kaled Zem into the Old Forest. Here Kallon, a Half-Elf of the Dunedain, found it whilst he recovered from a long pursuit of a band of Orcs. Kallon was caught between breaking off his hunt to head towards Sutur to learn more about the Crown and finding the hiding place of the cursed Orcs. Unfortunately he chose poorly, deciding to chase the Orc band back to their home. As he entered an old dwarven hall he was surprised by Balor. Balor was the servant of Demogorgon who had slowly discovered many of the dwarrowdelfs in Kaled Zem. He recognised the Crown immediately and slew Kallon for it.
824 The Gem of Law - Deep within the ancient halls of Kaled Zem Balor discovers the Gem of Law. Not in the least bit aligned with the Gem, Balor is torn between hiding it and declaring it to his master. Believing that he may somehow master its power, Balor hides the Gem and builds even greater protection around it.